Magnetic microscale and mesoscale devices, such as capsule endoscopes and microrobots, can be manipulated with an externally generated magnetic field. The magnetic field applies a combination of force and torque to the device without a mechanical connection. Magnetic manipulation systems have been used to drag a device along a path, roll a device across a surface, or point a device in a desired direction, such as magnetic catheters and magnetotactic bacteria.
Magnetic manipulation systems have incorporated permanent magnets and electromagnets. Although the dipole moment magnitude of a typical electromagnet can vary through a change in electrical current, the dipole moment orientation of such an electromagnet can be cumbersome to move dynamically. On the other hand, the dipole moment orientation of a permanent magnet is typically easier to move dynamically, but its dipole moment magnitude is fixed.
A combination of permanent magnets and electromagnets can be used to produce a suitable magnetic field for a manipulation task. Some tasks, however, tend to be better suited to either permanent magnet or electromagnet systems. For example, because electromagnet systems have more direct control of field strength, they have been used for multi-degree-of-freedom levitation and positioning control. Permanent magnets, which require no electrical power to generate a field, are well-suited for pulling or rolling tasks that require the magnetic source to move along complex trajectories.